1. Field of the Invention
The present invention is directed to a cassette for an infusion pump which may be inserted into and removed from the pump. More particularly, the present invention relates to an infusion pump cassette having a unitary injection molded elastomer conduit for fluid transport with a medical infusion pump.
2. Background and Description of Related Art
An infusion pump is used to automatically administer liquid medicant to a patient. The liquid medicant is supplied from a source of medicant and pumped into the patient via a catheter or other injection device. The manner in which the liquid is infused is controlled by the infusion pump, which may have various modes of infusion, such as a continuous mode in which the liquid medicant is continuously infused at a constant rate; or a ramp mode in which the rate of infusion gradually increases, then remains constant, and then gradually decreases. With the cost savings that may be attained today using home health care, small portable medical infusion pumps have become common for use in home treatment to provide for instance chemotherapy, pain management, and the like. These treatments often require the controlled infusion regimens discussed herein.
Portable medical infusion pumps typically run open loop for displacing a volume of medicament fluids with the peristaltic pumping mechanism of the medical infusion pump. The pump chamber of the infusion pump cassette displaces predetermined amounts of the medicament fluids infused with the stroke volume defined by the elongated tubular sections of the fluid transport swept through the conduit of the pump cassette which supports the elongated conduit. Thus, volumetric flow rate is determined in part by the controlled dimensional tolerances of the elongated tubular section inner diameter and length. A cassette utilized by the infusion pump is typically disposable, and thus must be manufactured in a cost effective manner, while requiring consistent cassette operation defined through the dimensional tolerances of the pump chamber provided by the cassette assembly.
Drugs being used with home therapy are increasingly becoming expensive for such things as therapies that may be involved in treatment of pulmonary hypertension, chemotherapy, and the like. Additionally, keep vein open (KVO) applications require replenishing of the liquid medicament supply periodically by a nurse or other medical professional which may from time to time visit the patient at home. It is important, therefore, to be able to know with a degree of certainty that the medicament is being delivered to the patient within a narrow therapeutic range for effective treatment for patients on closely monitored treatments. Also, where the medications are costly, it would be advantageous to be assured that the leftover drugs of the medicament bags are minimal to avoid waste, since after they are used in treatment, these drugs must be discarded and cannot be recycled for later use.
Additionally, the medicament liquid should not become depleted prior to the arrival of medical personnel for replacing the regimen. In the case of a KVO application, premature termination of the application may result in clotted access devices which are blocked by blood clots requiring considerable additional effort by the medical personnel responsible for the home therapy. Thus, it is important to maintain tight tolerances for and improve the accuracy of such portable medical infusion pump equipment.
One such cassette or module which may be inserted into and removed from the pump, is disclosed in U.S. Pat. No. 5,257,978 to Haber et al. A module disclosed by Haber et al. receives a length of an intravenous line in its interior, and a length of silicone tubing is connected to the intravenous line to form a single continuous conduit. The module is insertable into an infusion pump, in the form of a peristaltic pump, via a door which may be opened and closed. The Haber et al. pump is constructed so that it will operate only when the door is completely closed.
Additionally, U.S. Pat. No. 5,551,850 to Williamson et al. discloses the use of an elastomeric conduit used in the pump chamber, which is intended to result in a uniform pump chamber discharge volume by using materials of a relating constant storage modulus or stiffness. The Williamson et al. pump chamber assembly includes a pump chamber made of polyurethane tubing which was selected for the pump chamber because of its ability to rebound and its stiffness creating a hydraulically rigid section that resists volume changes due to system pressure variances.
The pump chamber assembly also includes inlet and outlet valve tubes coupled to the pump chamber, and inlet and outlet clips separate from the pump chamber and valve tube for securing the pump chamber to the cassette module of the infusion pump. Williamson et al. teach the use of particular materials not only for their mechanical properties, but also for the ability to solvent bond the component materials to other component materials of the assembly. Although Williamson et al. acknowledge that silicone has desirable features, including a relatively constant storage modulus or stiffness and a relatively low dynamic mechanical analysis tangent versus temperature over a range of operating temperatures, however, the silicone is considered to be difficult to solvent bond to other materials and therefore not suitable in a multicomponent solution. The use of solvent bonded materials in the pump chamber however adds cost to the manufacture and increases the difficulty of assembly of the pump chamber for use in the medical infusion pump cassette module, as well as, creating the possibility for malfunction due to failure of the solvent bond between materials. Therefore, it would be desirable to provide a unitary molded elastomer conduit for use with the pump chamber of the infusion pump cassette module, which improves the manufacturability and reliability, as well as the cost of the overall medical infusion pump system.